When I dropped my 727 pan earlier this year to have it powder-coated (both sides) I looked through rock auto's offerings for gaskets, I wasn't interested in any cork or cork-composite gaskets, the only one that seemed 100% synthetic was ATP GT10 (about $5). That's what I got. I spread some silicone dielectric grease on it when I installed it, I also changed the shift-lever seal. Nothing has leaked. I had to tweak the connections for the new lines I bent and installed, but nothing leaks now, that's just what I wanted.
Rockauto's photo of the gasked shows a highly rugged surface, like heavy orange peel, but that's not what this gasket looked like. It was totally smooth.
I also bought a new trans filter, it probably came with a cork gasket (or 2 gaskets, for 904 and 727) but it was cheap and I just used the filter.
If you buy the ATP TF30 kit (like $7) it comes with the filter and probably the same gasket I used (ATP GT10).
Right now there's an AUTO EXTRA 61658707 filter/gasket kit on wholesaler discount for like $1.50, gasket also looks like non-cork.